In Orange County, they just built a $481 million plant to purify sewage to such a degree that you can drink the output; they are going to inject it back into the ground to refill the aquifer. Others think this is a bad idea, that it is unlikely to win public acceptance, and may be dangerous. The phrase "toilet to tap" is not particularly appetizing, but the stuff is tested clean going out and coming in. (see earlier post here)
They already do it in Africa, Singapore and the UK, and are planning it in Australia. One concern is that people may turn back to bottled water just when we are making headway in convincing them to drink tap.